1. Field of the Invention
This invention relates to the autoxidation of alkyl aromatic compounds and is more particularly concerned with an improved process for the preparation of hydroperoxyisopropylphenyl esters, including novel bis(hydroperoxyisopropylphenyl)carbonates and bis(hydroxyphenyl)carbonates produced therefrom, and further relates to an improved process for the preparation of di- and trihydric phenols via said hydroperoxyisopropylphenyl esters.
2. Description of the Prior Art
The autoxidation of cumene and cumene type hydrocarbons to cumene hydroperoxide and the like is a well known procedure; see, for example, U.S. Pat. Nos. 2,820,064, 2,954,405, 3,634,328, and 3,803,243. U.S. Pat. No. 3,666,815 discloses similar type oxidation procedures leading to alcohol products and U.S. Pat. No. 3,816,548 shows the catalytic oxidation of isoparaffin hydrocarbons to alcohols using techniques similar to those described for the aromatic compounds.
Kropf et al (Liebigs Ann. Chem. 1975, 2010-2022 and J. Prakt Chem. 9, 173-86, 1959) have disclosed the use of metal phthalocyanines as catalysts in oxidizing cumene type hydrocarbons to cumyl hydroperoxides.
When an oxygen substituent, as in the case of an isopropylphenyl ester, is attached to the aromatic ring the autoxidation of the isopropyl group to the .alpha.-cumyl hydroperoxide derivative is complicated by the formation of side products and yields or conversions tend to be lower. Generally speaking, this is attributed to the presence of trace amounts of phenolic impurities which can arise from the hydrolysis of the phenyl ester.
Hydroperoxides of difficulty saponifiable esters of isopropylphenols are prepared in the liquid state with an oxygen containing gas at a temperature of about 20.degree. C. to about 125.degree. C. in the presence of an antacid as shown in U.S. Pat. No. 2,799,695. Reaction times are very long, of the order of days, while conversions are low.
U.S. Pat. No. 2,799,698 discloses the oxidation of p-isopropylphenyl acetate directly to hydroquinone diacetate in the presence of acetic anhydride.
The autoxidation of difficultly hydrolyzable esters of .alpha.,.alpha.-dialkylmethylphenols is reported in U.S. Pat. No. 2,799,715 by contacting said esters with an oxygen gas at 20.degree. C. to 125.degree. C. in the presence of an antacid. The hydroperoxides so formed are converted to the corresponding dihydric phenols. As in the case of U.S. Pat. No. 2,799,695, the reaction times are very long with low conversions.
Zimmer (U.S. Pat. No. 3,028,410) discloses the autoxidation of various isopropylphenyl esters to hydroperoxide derivatives. Reaction conditions include high reaction temperatures of 140.degree. C. to 160.degree. C. which is considered to be a high range when working with organic peroxidic materials; mono or dihydroperoxides of isopropylaromatic compounds are disclosed as catalysts. Conversions are reported on the basis of total hydroperoxide content of the reaction mixture alone. U.S. Pat. No. 2,954,405 broadly discloses the use of combinations of metal phthalocyanines with hydroperoxides in the autoxidation of alkyl aromatic compounds.
The hydroperoxyisopropylphenyl esters disclosed in the art cited above serve as intermediates for the preparation of dihydric phenols by the acid catalyzed rearrangement of the hydroperoxyisopropyl compounds to the corresponding hydroxyphenyl esters and acetone and subsequent saponification of the hydroxyphenyl ester to the dihydric phenol; see U.S. Pat. No. 2,799,695, 2,799,715, and 3,028,410.
It has now been discovered that isopropylphenyl esters can be autoxidized with essentially no induction period at a much faster rate with a higher conversion and selectivity and higher isolated yield of desired hydroperoxide product than has hitherto been possible while operating at relatively low and safe temperatures. Furthermore, the more facile preparation of the hydroperoxyisopropylphenyl esters provides for an improved means for the preparation of di- or trihydric phenols in overall increased yields.